Electrochemical display devices of various types are generally well known and have come into extensive use in products such as digital display watches and video game display panels. Typically, the display effect in such devices is achieved by changing the electrical potential of a display electrode relative to a counter electrode in the device to cause a film or a fluid filled cell on the display electrode to electrochemically change color. Such electrochemical display devices are superior to either the type of emitting diode or plasma display panels that preceded them in development, because they require substantially less power to achieve the display function. While liquid crystal display devices have been developed with lower power requirements than those of light emitting diodes and plasma display panels, they have other inherent disadvantages. For example, the visual effect achievable from liquid crystals is severely limited by the viewing angle, i.e. if viewed from an angle several degrees away from an axes orthogonal to the plane of the display surface the visibility of this display is significantly decreased. Also, liquid crystal displays have essentially no residual memory function within the liquid materials.
In the earliest electrochemical display devices, a color change was typically affected between a single dark color and a white or yellowish color, but no other variations in color were achievable. The electrochemical color change cells of the present invention have a wide color variation.
Electrochemical display devices are expected to have a bright future since the color of indication is brilliant, necessary voltage and current are small and there is no restriction on the observation angle.
Applicants have discovered unique types of electrochemical compounds. Applicants have synthesized for the first time an intramolecular charge transfer salt (which is described herein below) having multiple oxidation states which also shows a wide variation in color change and wide variation in the ultraviolet absorption. Applicants have also discovered for the first time intermolecular charge transfer salts (which is described herein below) including as an acceptor, a constituent, having a carbonyl group conjugated to an aromatic moiety.
An intramolecular charge transfer salt is a covalent compound containing a moiety having a negative charge and an unpaired electron (radical-anion) and moiety having a positive charge and an unpaired electron (radical-cation) on the same molecule. An intramolecular charge transfer salt is schematically represented in FIG. 15. Covalent compound 220 has a moiety 222 which has a negative charge and an unpaired electron 224. Moiety 222 is the radical-anion. Covalent compound 220 has a moiety 226 which has a positive charge and an unpaired electron 228. Moiety 226 is the radical-cation. A radical-anion/radical-cation covalent compound has not been synthesized prior to the synthesis by the applicant. The article in J. Am. Chem. Soc. 1983, 105, 4468-4469 to J. Becker et al. and the article in Chemistry Of Materials, 1989, 1, 412-420 to J. Becker et al. describe expected benefits of intramolecular charge transfer salts and reports some experimental data on a model system. However, the articles of Becker et al. do not teach or suggest the synthesis of an intramolecular charge transfer salt.
In recent years there has been an extensive amount of work on intermolecular charge transfer salts. This work is reviewed in the following articles; NATURE Vol. 109 May, 1984, p. 119, entitled "Organic Metals" to Bryce et al.; Accounts of Chemical Research, Vol. 12, No. 3, March, 1979, J. B. Torrance; The Organic Solid State, Jul. 21, 1986, C & EN p. 28, D. O. Cowan et al. The most highly studied intermolecular charge transfer salts are salts of TCNQ (tetracyano-p-quinodimethane), in particular the intermolecular charge transfer salt of TCNQ with TTF (tetrathiafulvalene). The TTF-TCNQ salt shows metallic-like conductivity. The prior art, however, does not teach nor suggest an intermolecular charge transfer salt including a compound having a carbonyl group conjugated to an aromatic moiety as an electron acceptor constituent. As used herein, an electrical conductor includes a material which is a semiconductor and a metallic conductor.
An intermolecular charge transfer salt is schematically represented in FIG. 16. Ionic compound 230 has anionic constituent 232 which has a negative charge and an unpaired electron 234. Constituent 232 is the radical-anion. Ionic compound 230 has cationic constituent 236 which has a positive charge and an unpaired electron 238. Constituent 236 is the radical-cation. Gap 240 schematically represents the absence of a covalent link or bond between the radical-anion constituent 230 and the radical-cation constituent in the ionic compound 230 and indicates the ionic interaction between the radical-cation and radical-anion.
It is an object of this invention to provide an electrochemical color change cell containing an intramolecular charge transfer salt as a color changing agent.
It is another object of the present invention to provide an electrochemical color change cell having as color change agent an intermolecular charge transfer salt containing a constituent having a carbonyl group conjugated to an aromatic moiety.
It is another object of the present invention to provide an intermolecular charge transfer salt compound.
It is another object of the present invention to provide intramolecular charge transfer compound containing a constituent having a carbonyl group conjugated to an aromatic moiety.
These and other objects, features and advantages of the present invention will be readily apparent to those of skill in the art from the following more detailed description of the preferred embodiments and the figures appended thereto.